In, for example, Patent Documents 1 and 2, there is disclosed a technology in which for assuredly igniting a mixture of is fuel and air in a combustion chamber, a voltage is repeatedly applied across electrodes of an ignition plug thereby producing a plurality of discharges.
In the technology of Patent Document 1, for example three side electrodes are arranged around a center electrode of an ignition plug and a voltage is pulsively applied to the electrodes thereby to produce a spark discharge between the center electrode and each of the side electrodes in turn. In this technology, by increasing the voltage application interval by a certain degree, a next discharge is forced to appear between the center electrode and one of the side electrodes without inducing a discharge between the center electrode and another one of the side electrodes that has just participated in producing the last discharge.
In the technology of Patent Document 2, prior to a main discharge that forms an arc discharge, a plurality of pulse discharges, which form streamer discharges or glow discharges, are carried out, so that the active species concentration is increased immediately before the arc discharge or main discharge.
In general, the active species are radicals (including excited condition of ion and bound electron), electrons, atoms, molecule internal oscillations, translation motions, etc. Since, after production by the discharge, these active species are transited to a stable condition with passage of time, the life of the active species is relatively short.
In general, in a combustion chamber of an internal combustion engine, there is a flow of air-fuel mixture or gas flow that is to be ignited. For example, in case of reciprocating internal combustion engines in which pistons move up-and-down, a gas flow is produced in each cylinder due to the up-and-down to movement of the piston. Particularly, in a lean air-fuel mixture that has a high air-fuel ratio or an air-fuel mixture that contains a large amount of exhaust gas recirculated through an EGR system, a combustion speed is lowered and thus the combustion is made unstable. Thus, in order to compensate the combustion instability, attempts for positively producing the gas flow are usually carried out. One of them is to provide in an intake passage a device that produces in each combustion chamber a gas flow such as tumble flow, swirl flow or the like, and the other of them is to make the gas flow more active by adjusting an open timing or open angle of the intake valves.
If such gas flow is present near an ignition plug, active species produced as a result of the discharge and flame cores (or kernels) are forced to flow downstream by the gas flow and thus, usually, ignition becomes much difficult. Patent Documents 1 and 2 take no thought of influence of such gas flow.
For example, in the method of Patent Document 1, due to a considerable influence of the gas flow, the discharge tends to take place at only a particular side electrode, which is an uneven distribution problem.
Furthermore, in the technology of Patent Document 2, in presence of the gas flow, the active species produced as a result of pulse discharge effected prior to the main discharge is forced to flow downstream, and thus, at the time when the main discharge is actually carried out, the active species fail to exist in large quantity around the main discharge, and thus, the effect of promoting a flame propagation due to the active species is lowered.
The present invention aims to provide an ignition device and an ignition method, which are able to more assuredly and effectively make an ignition to an air-fuel mixture in the presence of the gas flow.